The present invention relates to a method of continuously swelling starchy raw materials, whereby the raw material is supplied at a temperature below the gelatinization point of the starch and under a mechanically increased hydraulic pressure to a section wherein it is swelled in a steep.
A method of this type is known from German Patent 3 110 464 and is technically termed "brief swelling." It is employed to obtain starch from grain, especially from maize.
To attain rapid water uptake, the raw material is subjected to swelling at a pressure of at least 5 bars, and of 10 to 50 bars for maize, for 2 to 3 hours prior to mechanical processing in a high-pressure device. Measured portions of processing water are added to granular maize, which is then continuously pumped to a swelling section in the form of a coil of pipe, in which the brief swelling occurs at a pressure of 10 to 50 bars, and preferably 15 bars, and at a temperature of 50.degree. to 60.degree.. At the exit from the swelling section is a tank that is provided with a filter. The excess water is extracted through the filter and a pressure-release mechanism decreases the pressure to break up the maize.
One drawback to the method is that the raw material and steep travel through the swelling section in the same direction, which makes it impossible to extract all of the soluble constituents, some of which are undesirable.
It has been discovered, that, although a pressurized plant with this type of design and operation is appropriate for the continuous swelling of milled cereal products, it involves considerable drawbacks in relation to whole-grain raw materials.
Unmilled and whole-grain raw materials can easily agglomerate and clog up a swelling section in the form of a coil, especially upstream of curves and constrictions, bottlenecking the overall system and requiring expensive manual cleaning. Another problem encountered with whole-grain raw materials involves the proposed approach of continuously extracting the product from the pressurized system while simultaneously breaking it up. Since decreasing the high pressure demands considerable reduction in the extraction-point cross-section of the pressure-release mechanism, that mechanism can also clog up completely or to some extent, making it difficult or impossible to break up the swollen product to a specific size. Furthermore, whole-grain raw materials cannot be extracted from the aforesaid pressure-release mechanism unaccompanied by a considerable proportion of steep, the loss of which increases the energy consumption of the plant.
Introducing the raw material into the pipeline with a pump is also a drawback because, in addition to the technologically requisite pressure elevation, enough power must be applied to force the raw materials through the coil, and the raw material backs up at the pressure end, causing wear in any appropriate type of pump.